Most people have seen clips of Martin Luther King Jr.'s "I've been to the Mountaintop" speech in Memphis where he died, but relatively few know that he was there as part of a sustained campaign to support an AFSCME strike of santitation workers demanding a union.  

In the dumbing down of celebrations of Martin Luther King Jr. as a national icon, the relatively radical demands for economic justice that he was making in his later years tend to disappear.  

But Martin Luther King Jr. had made a strike of public employees in Memphis a centerpiece of his efforts to launch the "Poor Peoples Campaign" of his final year.  You can read more details about the strike at this website commemorating the strike, but it's worth understanding that Martin Luther King Jr., even as he rightly criticized the exclusionary rules of some individual unions, always saw a strengthening of unions and labor as critical to achieving long term justice for African Americans.  

As this archive details, in his whole career he saw unions as critical.  A few excerpts:

Less than a century ago the laborer had no rights, little or no respect, and led a life which was socially submerged and barren....American industry organized misery into sweatshops and proclaimed the right of capital to act without restraints and without conscience. The inspiring answer to this intolerable and dehumanizing existence was economic organization through trade unions...

By raising the living standards of millions, labor miraculously created a market for industry and lifted the whole nation to undreamed of levels of production. Those who attack labor forget these simple truths, but history remembers them...

That is why Negroes support labor's demands and fight laws which curb labor. That is why the labor-hater and labor-baiter is virtually always a twin-headed creature, spewing anti-Negro epithets from one mouth and anti-labor propaganda from the other mouth.
--Speaking to the AFL-CIO on Dec. 11, 1961

He attacked anti-union right-to-work laws:

In our glorious fight for civil rights, we must guard against being fooled by false slogans, such as 'right to work.' It is a law to rob us of our civil rights and job rights. It is supported by Southern segregationists who are trying to keep us from achieving our civil rights and our right of equal job opportunity. Its purpose is to destroy labor unions and the freedom of collective bargaining by which unions have improved wages and working conditions of everyone...Wherever these laws have been passed, wages are lower, job opportunities are fewer and there are no civil rights. We do not intend to let them do this to us. We demand this fraud be stopped. Our weapon is our vote."
--Speaking on right-to-work laws in 1961

If you want to honor Martin Luther King Jr., you should honor the labor struggles, including those of public employees demanding just economic treatment.  Martin Luther King Jr. never separated collective organization of black workers (along with white workers) from the demands for equal treatment of individuals in the workplace.   Most memory of Martin luther King Jr. emphasizes only individual equality but his legacy, including his death, was also dedicated to the collective organization and empowerment of workers.